This invention relates to a communication protocol and interface circuit for communication between a host device and a driver device using a single wire interface, more commonly known as a 1-wire interface.
Light-emitting diodes (LEDs) are being used increasingly in display devices and numerous lighting applications. For example, some liquid crystal display (LCD) devices use white LEDs as the backlight for the LCD display. These LEDs are typically driven by an LED driver that functions as a constant current device to supply a constant sink current fed through the LEDs to provide a constant luminescence. Alternatively they can function as an average current device to supply a switching pulse width modulation sink current fed through the LEDs to provide a dimming luminescence. The amount of constant sink current driving the LEDs by the LED driver is typically controlled by a host controller residing in an electronic device (e.g., a mobile telephone, computer, etc.) that utilizes the LEDs.
The host controller interfaces with the processor of the electronic device to provide pulse width modulation (PWM) commands directing the average intensity of illumination to be generated by the LED driver, and sends the PWM signals to the LED driver to adjust the average current for driving the LEDs. The host controller also communicates with the LED driver to send a variety of commands to the LED driver to program the LED driver. These commands include commands for setting the DC current to be provided by the LED driver to the LEDs.
Conventional communication protocols and interface circuitry between a host controller and a LED driver require two separate communication channels (e.g., two wires, each wire with its own set of integrated circuit pins) for communication of the PWM signals and the commands for programming the LED driver. Conventional 1-wire communication protocols are typically used by the host controller to communicate commands for programming the LED driver based on the number of pulses sent via the 1-wire interface. All pulses sent over the conventional 1-wire interface are typically interpreted as commands. The conventional 1-wire communication protocols cannot be used for dynamic communication of PWM signals to adjust the average current for driving the LEDs. Thus, in addition to the pin used by the 1-wire interface to receive commands from the host controller, conventional LED drivers require an additional control pin on the LED driver integrated circuit (IC) to receive PWM pulses for adjusting the average LED drive current. This adds to the complexity and manufacturing cost of the LED driver and host controller ICs.